Recent Linux newbie here...
Being a newbie I opted for Mandrake 9.2 from the recommendations of the people on here an elsewhere.
Installed it and it worked without a hitch on my PowerEdge 400SC server.
It depends on what you are going to use Linux for... configuring some of the add-ins like Samba, PHP etc takes alot of reading and tweaking. I finally got Samba setup correctly and it is working ... now it is time to move on to PHP and SQL
One word of advice... if you are planning on setting up Samba to connect to other windows machines... during the installation of Mandrake.. change the hostname to something other than localhost.